Wafer coating system

ABSTRACT

Semiconductor wafers having patterns of steps and grooves defining microcircuit elements thereon are coated with metallic film by supporting the wafers individually adjacent a respective ring-shaped sputtering source in stationary relationship thereto. To effectuate such individual wafer processing on a continuous basis and preserve the evacuated argon environment, a vacuum chamber sputter coating apparatus is provided which has a number of work stations therein, at least one of which includes said ring-shaped sputtering source. Also included is a load lock; and an intermittently rotating vertical plate-like wafer carrier means therewithin positioned closely adjacent the chamber entrance, and carrying wafers in turn from the load lock to the work stations. The carrier includes apertures each accepting a wafer therewithin in an upright position, with the wafers edgewise resiliently supported by clip means, without the use of any externally-originating supports such as platens. Both surfaces of the wafer can be accessed by processing equipment, for example, heating or cooling means at some of the work stations. Only a few wafers inside the chamber are at risk at any one time, and introduction of contaminants, debris, as well as disturbances to the chamber environment are minimized.

This application is a division, of application Ser. No. 106,343, filed12/21/79 now U.S. Pat. No. 4,756,815.

BACKGROUND OF THE INVENTION

The present invention relates to the coating of thin substrates bydeposition under vacuum. More particularly, the field of the inventionis metallization of semiconductor wafers, and apparatus for effectingsuch metallization of wafers individually, and on a serial, continuousbasis. Semiconductor wafer fabrication techniques have evolved rapidlyover the past decade. Individual microcircuit devices have becomeprogressively smaller, thereby increasing the number of such devicesthat can be put onto a wafer of a given size. Additionally, wafers oflarger diameter are coming into use. A few years ago wafers of 2-inchdiameter were commonplace, and 3-inch diameter wafers were consideredlarge. Today much of the device fabrication is done with 4-inch diameterwafers and widespread use of 5-inch wafers within a very few years isforeseen. The reductions in device size, coupled with the increased sizeof wafers, have served to greatly increase the economic value ofindividual wafers, and thus the need to process and metallize suchwafers in an improved manner.

Most semiconductor and microcircuit fabrication techniques requiredeposition of metallic coatings of high quality upon the semiconductorwafer upon which the microcircuits are defined. Whether a coating is of"high" quality will of course ultimately be determined by the degree ofsatisfaction with the ultimate yield of microcircuit devices from thewafer, and their utility, for example, as meeting the higher military orindustrial standards, or the lesser consumer and hobbyist standards.Although therefore difficult to quantify, it is generally agreed thatmetallization quality, and thus ultimate quality and quantity of yield,will in turn be a function of the following factors: uniformity ofcoverage upon the uppermost and main planar surface of the wafer("planar coverage"); contamination levels incorporated into the finalcoating; defect level caused by debris; symmetry and homogeneity, or inother words freedom from "layering" and the manner of distribution ofcontaminant levels in the film; the degree of reproducibility andcontrol, especially of temperatures during coating deposition; and stepcoverage, that is, the continuity and evenness of the coating across notonly the main plane of the surface, but also the sides and bottoms ofsuch features within the surface as steps, grooves, depressions, andraised portions which define the microcircuits.

Some of these characteristics are harder to achieve or are more criticalthan others, or have been thought to require definite specializedprocessing steps to achieve. For example, because of the constraints ofgeometry, step coverage has been a particularly difficult requirement tofulfill. The sidewalls of the steps and grooves are generallyperpendicular to the uppermost surface of the main plane of the wafer,and may face both inwardly and outwardly of the wafer center. Coveringof such perpendicular surfaces, particularly the outer-facing ones,while at the same time covering the planar surfaces, is obviously anespecially difficult problem, yet such "step coverage" is of particularimportance in determining the quality of the metallization overall. Ithas generally been thought that in order to achieve the requireduniformity of planar surface coverage as well as adequate step coverage,relative motion between the wafers and the deposition source duringcoating deposition is necessary. However, such motion carries with itcertain disadvantages, especially the heightened possibility ofgeneration of debris, as by dislodgement of deposits of coating materialon various internal structures of the apparatus due to the motion, aheightened possibility of mechanical shock and vibration damage to thewafer, and the build-up of deposition on the wafers in a nonsymmetricaland inhomogeneous fashion, as will be further explained below.Naturally, contamination level will depend on the maintenance of thequality of the vacuum environment during deposition and theconcentration of contaminants relative to the speed of deposition. Thusthe adequacy of "outgassing", or the evacuation of gas and vapors fromthe wafer and accompanying wafer supports which are introduced into thecoating chamber will also be important.

The manner in which the prior art has attempted to achieve one or moreof the above characteristics, and the attendant difficulties andtrade-offs involved in achieving the above criteria of coating quality,may be best appreciated by considering the two main types of vacuumdeposition systems which are in current use for metallizing wafers batchand load lock. A typical batch system comprises a pumping station, anevacuable bell jar, an isolation valve between the pumping station andthe bell jar, heat lamps, one or more deposition sources, and planetaryfixtures which hold the semiconductor wafers and rotate them above thedeposition source or sources. At the start of a deposition cycle theisolation valve is closed and the bell jar is open. Wafers are loadedmanually from cassettes into the planetary fixtures (a load of 75 wafersof 3-inch diameter is typical). The planetary fixtures are then mountedin the bell jar, the bell jar closed, and the system evacuated. After aprescribed base pressure is reached, the wafers are further outgassedthrough the application of radiant energy from the heat lamps. In somecases the wafers are sputter-etch cleaned prior to the start ofdeposition. A typical coating is aluminum or an aluminum alloy sputteredonto the wafer to provide interconnect metallization. In order toachieve the required coating uniformity and step coverage, relativemotion is provided by rotation of the planetary fixtures Afterdeposition, the wafer and system are allowed to cool, the isolationvalve is closed, the bell jar vented to atmosphere, the bell jar opened,and the planetary fixtures are removed and unloaded manually intocassettes. This completes a typical cycle, which takes approximately 1hour

Although such batch systems are in widespread use in production todayfor metallizing semiconductor wafers, certain of their characteristicspose limitations and disadvantages. For one, the entire relatively largebatch of wafers is inherently "at risk" of a partial or total lossduring the deposition cycle. The manual loading of wafers from cassettesinto planetary fixtures provides ample opportunity for contamination andbreakage. Air exposure of the entire system inside the bell jar forloading and unloading leads to possible contamination and adds a verylarge outgassing load for the vacuum pumps to contend with (theoutgassing area ascribable to the wafers alone is typically less thanten percent (10%) of the total air-exposed area which must beoutgassed). Long deposition throw distances (typically 6 to 14 inches)from the source are needed to obtain the large area coverage for themany wafers to be coated within the batch system. This leads to lowdeposition rates (typically 600 angstroms per minute for sputterdeposition source), which make the films more susceptible to poisoningby reaction with background gases, and thus more sensitive to thequality of the evacuated environment. Outgassing of the wafers and theair-exposed areas of the system is accelerated by application of radiantenergy from heat lamps, but since the wafers are in uncertain thermalcontact with the planetary fixtures, their temperatures are alsouncertain. Moreover, the heating source normally cannot be operatedduring sputter deposition, so that the wafers cool in an uncontrolledfashion from the temperature attained during preheat. Lack of control ofwafer temperature during deposition limits certain aspects of filmcharacteristics which can be reliably and reproducibly attained. Ofcourse the mechanical motion of the planetary fixtures for achievinguniformity and step coverage can dislodge particles of coating materialdeposited elsewhere within the system other than on the wafers, which inturn can cause debris to become attached to the wafers, in turn reducingyield of good devices.

A typical load lock system comprises a pumping station, an evacuableprocessing chamber, an isolation valve between the pumping station andthe processing chamber, a heating station, a deposition source, a loadlock, and a platen transport system. At the start of a deposition cycle,wafers are loaded manually from a cassette into a metal platen (a12-inch by 12-inch platen size is typical), which then acts as a carrierfor the wafers during their journey through the load lock and processingchamber. After introduction through the load lock into the processingchamber, the platens and wafers are transported to the heating station,where they are further outgassed by the application of radiant energy.Additional cleaning of the wafers by means of sputter etch may also beperformed at the heating station. Metal film deposition is accomplishedby translating the platen and wafers relatively slowly past thedeposition source, which may be a planar magnetron type of sputteringsource with a rectangular erosion pattern, with the long dimension ofthe erosion pattern being greater than the platen width. Relatively highdeposition rates (10,000 angstroms per minute) are achieved by movingthe platen past the sputter source over a path which passes the waferswithin several inches of the sputter source. After deposition, theplaten and wafer are returned to the load lock where they pass from theprocessing chamber back to atmosphere. The wafers are then unloadedmanually back into a cassette. This completes a typical cycle, whichtakes typically 10 to 15 minutes. In another type of load lock system,the wafers are mounted on an annular plate which rotates past thedeposition source. Each wafer makes multiple passes below the depositionsource until a film of sufficient thickness is built up.

The above load lock systems overcome some of the disadvantages of batchsystems, but not all. Of primary importance is the fact that the use ofa load lock allows wafers on a platen to be introduced into and removedfrom the processing chamber without allowing the processing chamberpressure to rise to atmospheric. This greatly reduces the amount ofair-exposed surface that must be outgassed prior to deposition. Whilethe processing chamber does need to be opened to atmosphere periodically(for cleaning and for replacing deposition targets), the frequency ofsuch air exposure is much less than with batch systems.

Another important factor is that the size of the wafer load which is "atrisk", that is, subject to being rejected due to a defect or failure ofthe process, is significantly smaller in the load lock system (16 3-inchwafers in the first load lock system, compared with 75 3-inch wafers inthe batch system in the above example). Because the number of wafers perload is much smaller with the load lock system, it is not necessary toemploy the long deposition throw distances required with batch systems.Higher deposition rates are therefore attainable by closer couplingbetween wafer and source.

Despite the advantages afforded by load lock systems, many disadvantagesand shortcomings still remain. In both batch and load lock systems,wafers are typically transferred manually between platen and cassette,with attendant risks of contamination and breakage. Although the use ofthe load lock avoids exposure of the processing chamber to theatmosphere, the platen which carries the wafers is air-exposed on eachload and unload cycle. Thus its surfaces must also be outgassed, whichraises the total outgassing load well beyond that of only the wafersthemselves. In addition, sputtered deposits that build up on the platenbecome stressed due to repeated mechanical shock and air exposure,leading to flaking and debris generation. As with batch systems, wafersare still in uncertain thermal contact with their carrier. Controls overwafer temperature during outgassing and during deposition remaininadequate. The metal films are put down on the wafers in anon-symmetrical fashion, since the film deposited on the wafer builds upin different ways depending upon its location on the platen, i.e.,whether the wafer is outboard, inboard, approaching the source, ormoving away from the source. Translation of the platen during depositionto provide uniformity and step coverage heightens the risk of generationof debris and flakes, and thus contamination of the wafers. In certainload lock systems, symmetry and homogeneity are further compromised bycausing the wafer to make multiple passes below the deposition source.Thus the metal film is deposited in a "layered" fashion because thedeposition rate tapers off to almost nothing when the wafers arerotating in a region remote from the deposition source. The low rates ofdeposition in such regions heighten the risk of contamination due toincorporation of background gases into growing film, andnon-uniformities in the distribution of any contaminants which may bepresent result from the non-uniformities in deposition rate.

Even though a much smaller number of wafers is being processed at anyone time in load lock systems as compared with batch systems, asignificant number of wafers still remains "at risk". From this point ofview, it would be best to process wafers individually on a serialcontinuous basis, but the time needed for adequate pumpdown of the loadlock during loading and unloading, and for wafer outgassing and theoutgassing of wafer supports, coupled with the time needed to coat awafer individually in an adequate manner, has rendered the concept ofsuch individual processing impractical until now as compared to batchsystems or load lock systems handling a plurality of wafers with eachload. It would also be much better from the viewpoint of prevention ofdebris generation and consequent reduction in yield of good microcircuitdevices, as well as lessening the risk of abrasion and mechanical shockand vibration, to hold wafers stationary during coating deposition.However, as we have seen, this has been considered inconsistent with theneed to obtain adequate deposition uniformity and step coverage, sincethis normally requires establishing relative motion between the sourceand wafer. Further, there has been no basis for expecting greatercontrol over reproducibility and temperature of the coating process in aindividual wafer processing system as opposed to a batch or load locksystem coating a plurality of wafers with each load.

Accordingly, an object of the invention is to provide apparatus forrapidly coating wafers individually with a higher quality coating thanpossible previously.

A related object of the invention is to provide apparatus for depositingmetallization layers of superior quality with respect to the aggregateconsiderations of step coverage, uniformity, symmetry and homogeneity,contamination level, debris damage, and reproducibility.

Also an object of the invention is to provide apparatus for rapidlycoating wafers individually with improved step coverage and gooduniformity.

Another related object of the invention is to provide an improved loadlock system for metallizing wafers individually yet at a high rate.

Yet another object of the invention is to provide an improved load locksystem for metallizing semiconductor wafers individually on aproduction-line basis with enhanced quality, including uniformity andstep coverage.

A related object is to provide a system for coating wafers which reducesthe number of wafers at risk at any one time due to processing.

Another related object is to provide a system for metallization or othervacuum processing of wafers individually on a serial continuous basis,with a plurality of work stations operating simultaneously on individualwafers.

Also a related object is to reduce the outgassing load and minimizedisturbance to the evacuated coating environment due to introduction ofwafers into a load lock system for coating.

Yet another object of the invention is to improve the yield ofmicrocircuit devices subsequently derived from the wafer by reducinggeneration of debris and the probability of damage from abrasion andincorporation of contaminants.

Yet another object is to provide a load lock type system whichaccomplishes transport between various work stations and into and fromthe vacuum regions without the use of platen-like supports for thewafers.

Also a related object of the invention is to provide a load lock typesystem as above which does not use platen-like wafer supports, in whichloading and unloading are effected of certain wafers while yet othersare being processed.

A further related object is to provide a system as above which iscompatible with automatic wafer handling from cassettes.

Also a related object is to provide improved control over wafers,especially their temperature, throughout the processing thereof.

Yet a further object of the invention is to provide a system forproduction-line use in which reliability, maintainability, and ease ofuse are improved.

SUMMARY OF THE INVENTION

The broadest objects of the invention are met by providing apparatus forcoating a wafer individually, which includes a ring-shaped sputteringsource emitting coating material and having a diameter larger than thatof one of the wafers, means for locating an individual one of the wafersin facing stationary relationship to the source, and at a distance lessthan the diameter of the source, as well as means for maintaining thesource and wafer in an argon environment of up to 20 microns pressure (1micron=10⁻³ millimeters of mercury=1 millitorr=0.133 Pa) during coatingof the wafer. In this manner a coating of improved quality with gooduniformity is rapidly deposited on the wafer without need for relativemotion between wafer and source and the added complexity and debrisgeneration risk attendant thereto.

The objects of the invention are also met by providing apparatus forrepetitively sputter coating individual wafers in minimal time, usefulwith vacuum chamber means continuously maintaining a controlledsubatmospheric environment. The apparatus includes internal wafersupport means positioned within the chamber immediately inside of theentrance thereof, including means for releasably and resilientlygripping edgewise an individual wafer, to immediately accept a waferupon insertion and permit instant release and removal upon completion ofcoating. Also included is a sputtering source mounted in the chamber andhaving a cathode of circular outline emitting coating material upon thewafer in a pattern approximating that from a distributed ring source.The source has a diameter which is larger than that of the wafer and isspaced from the wafer by a distance less than that of the sourcediameter. The wafer support means holds the wafer stationary duringcoating. Finally, the apparatus includes load lock means including amovable member within the chamber to seal the wafer support means offfrom the remainder of the chamber interior and when the door of theentrance is opened, isolating the wafer and support means from thechamber environment during insertion and removal of a wafer. In thismanner, individual coating of wafers can be repetitively performed, withdisturbances to the chamber environment by outside wafer supportexpedients, consequent contaminants, and large load lock volumesminimized, while overall wafer coating time is improved.

Objects of the invention are also met by apparatus for individuallyprocessing wafers continuously in a controlled subatmosphericenvironment, which includes a vacuum chamber having a first opening in afirst wall thereof and a door for closure of the opening, at least onewafer processing means mounted in a wall of the chamber and defining atleast one processing location of the chamber spaced from the firstopening, and movable carrier means within the chamber movable betweenthe first opening and the processing location. The carrier means isprovided with at least two apertures and spaced a first distance toenable the apertures to be aligned respectively with the first openingand the processing location. Each of the carrier apertures mounts clipmeans for releasably and resiliently gripping a wafer. The apparatusalso includes closure means within the chamber for closing off one ofthe carrier apertures when said aperture aligns with the first chamberopening, the closure means and chamber defining therebetween a smallload lock volume with the closure means sealing off the aperture fromthe chamber when the chamber door is opened to load or unload a waferinto the clip means. In this manner wafers can be continually seriallyintroduced into the vacuum chamber with minimal disturbance of thecontrolled atmosphere therein, and the wafers individually processed atthe processing location while loading and unloading of another wafertakes place at the load lock without use of external wafer supportmeans, the presence of which would greatly increase the gas load to beeliminated by the load lock and chamber, as well as increasing thepossibility of contaminants. Furthermore, the load lock volume isminimized to only that absolutely necessary to accommodate a singlewafer, thus also reducing the amount of pumpdown load for the load lockand chamber.

In one preferred embodiment, the movable carrier means may be providedin the form of a disc-like transfer plate mounted for rotation about itsaxis with various wafer processing stations symetrically disposed aroundthe same axis. Besides sputtering stations, the stations may also beheating or cooling stations, and the heating, for example, may beapplied to the side of the wafer opposite that of the sputteringdeposition, since the clip means support the wafers edgewise, therebyallowing processing of both sides thereof. The wafer transfer platepreferably rotates in a vertical plane to better combat accumulation ofdebris on the wafers. When fully loaded, the apparatus limits the numberof wafers at risk at any one time to only those loaded in the wafertransfer plate, and enables several processing operations to be carriedon at the same time, for example, coating of one wafer simultaneouslywith the heating of another and with the unloading and loading of stillothers. The use of the internal wafer clip support means, thin loadlock, and individual processing of wafers enables easy loading andunloading, including simplified automatic loading. In one particularaspect, a vertically-acting blade-like elevator means raises a waferedgewise to a point immediately adjacent the chamber entrance. Vacuummeans associated with the door of the chamber then grip the rear surfaceof the wafer and propel same into the clip means as the door is closed,thereby loading the load lock and sealing same simultaneously. Furtherdetails of a fully automatic system for loading the vacuum processingchamber from a conveyor-driven cassette containing a plurality of wafersto be coated may be found in the co-pending application of G. L. Coad,R. H. Shaw, and M. A. Hutchinson for "Wafer Transfer System", filedcontemporaneously herewith, now U.S. Pat. No. 4,311,427. Similarly, thedetails of the means for resiliently supporting the wafers within thevacuum chamber and associated means for aiding the loading and unloadingof same into said supports within a chamber may be found in theco-pending application of R. H. Shaw for "Wafer Support Assembly", filedcontemporanously herewith, now U.S. Pat. No. 4,306,731.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view of the complete wafer coating system ofthe invention, showing the main cylindrical processing chamber, the doorarrangement at the entrance of the load lock to the chamber, and thefour remaining work stations of the processing chamber, together withportions of the wafer cassette load/unload assembly;

FIG. 2 is a broken-away perspective view of the processing chamber ofFIG. 1, showing the load lock and sputter coating stations in moredetail;

FIG. 3 is a perspective view of the cassette load/unload assembly ofFIG. 1, showing its manner of cooperation with cassettes ofvertically-oriented wafers and the door assembly of the processingchamber, and the manner in which wafers are transferred therebetween andinto the chamber load lock;

FIG. 4 is a cross-sectional elevational view of the door and load lockof FIGS. 1 through 3, showing the manner in which the door assemblyloads a wafer into the load lock, and the manner in which the load lockis sealed from the remainder of the processing chamber interior;

FIG. 5 is a view similar to FIG. 4, showing the relative positions ofthe elements of the load lock upon completion of loading of the wafertherewithin;

FIG. 6 is a view similar to FIGS. 4 and 5, showing the position of thewafer and the load lock elements just subsequent to the extraction of awafer from the internal wafer support assembly, and prior to the openingof the door, or just before the loading of a wafer into the internalwafer support assembly immediately after closure of the door forloading;

FIG. 7 is a cross-sectional elevational view taken across line 7--7 ofFIG. 1, showing a wafer heating station within the chamber of FIG. 1;

FIG. 8 is an elevational cross-sectional view taken along line 8--8 ofFIG. 1, showing a wafer cooling station within the wafer processingchamber of FIG. 1;

FIG. 9 is a cross-sectional elevational view taken along line 9--9 ofFIG. 1, showing the wafer sputtering station of the chamber of FIGS. 1and 2;

FIG. 10 is a schematic cross-sectional view focusing on the wafer andsputtering source target of FIG. 9, which shows the spatialrelationships, relative positioning, and dimensions of these elements ingreater detail;

FIG. 11 is a graph illustrating the uniformity of thickness ofdeposition on the main planar surface of the wafer by the source ofFIGS. 9 and 10 as a function of the radial position on the wafer, foreach of several wafer-to-source distances;

FIG. 12 is a plot similar to FIG. 11, but for only a singlewafer-to-source distance, one curve being for a deposition environmentof 2 microns argon pressure and the other being for a depositionenvironment of 10 microns argon pressure;

FIG. 13 plots thickness of coating coverage on the sidewall of grooveswithin the wafer surface as a function of the radial position on thewafer, both for outwardly-facing (relative to the center of the wafer)sidewalls, as well as inwardly facing sidewalls, for a source-to-waferdistance of 4 inches, one curve being taken at 10 microns argonpressure, and the other at 3 microns argon pressure;

FIG. 14 is a plot similar to FIG. 13, except that the source-to-waferdistance is 3 inches;

FIG. 15 is a plot of uniformity of planar coverage as a function ofargon pressure of the coating environment, one curve being for theradial position 1.5 inches, and the other being for the radial position2.0 inches.

DETAILED DESCRIPTION

The wafer coating system of FIG. 1 principally includes a generallycylindrical vacuum processing chamber 10 having five work stations, oneof which comprises load lock arrangement 12; and one of which comprisescoating station 14. Remaining further elements of the coating systemfound within chamber 10 may be seen in more detail in FIG. 2, which alsoshows a wafer 15 within load lock 12; and also a wafer at coatingstation 14. Further elements include pressure plate 16, wafer carrierplate assembly 18, and clip assemblies 20 (better shown in FIG. 3), bywhich a wafer is retained within wafer carrier plate 42 of carrier plateassembly 18. Door assembly 22, which seals the entrance opening 23 ofchamber 10, and which cooperates with the just mentioned elements toform the chamber load lock arrangement 12, completes the principalelements of processing chamber 10. These elements, together withcassette load/unload assembly 24 and the various ancillary vacuum pumps25 for chamber and load lock evacuation, and control means, are allhoused compactly in cabinet 26.

The system desirably includes several other work stations other thanload lock arrangement 12 and coating station 14, in particular waferheating station 28, auxiliary station 29, and wafer cooling station 130.All five work stations are equally spaced laterally from each other andfrom the central axis 36 of the vacuum chamber. Although five stationsare provided, the design could be equally well adapted, to both agreater or fewer number of stations. Also included are at least twopneumatic rams 30 and 31 which function to drive pressure plate 16 andwafer carrier plate assembly 18 against the front wall 32 of chamber 10,and carrier plate drive 35, which centrally mounts carrier plateassembly 18, which is circular and of nearly the diameter of front wall32, for rotation about the central axis 36 of the vacuum processingchamber.

In general, wafers are individually presented and loaded by doorassembly 22 into load lock arrangement 12 and thereby within wafercarrier plate 42. The wafer is then passed in turn to each of the workstations, where it is heated for completion of outgassing and/orsputter-etch cleaned, coated, optionally coated with a second layer,cooled, and then returned again to load lock 12 for removal from wafercarrier plate assembly 18, again by door assembly 22. Although theforegoing generally-described system is a rotary one and a multi-stationone, the load lock and coating steps are equally applicable to a singlestation or dual station configuration, or a non-rotary or in-linearrangement as well.

Now considering the system in more detail from the view point of anincoming wafer, the load lock arrangement 12 through which a wafer 15must be passed in order to enter the evacuated environment of thechamber is of key importance. FIGS. 4-6 are especially important inappreciating the operation of the movable elements of load lock 12. Aspointed out above, the load lock is defined by a sandwich arrangement ofelements between the chamber door assembly in its closed positionagainst the front wall of the processing chamber and the pressure platein its driven position. The load lock is built around a circularaperture 37 within wafer carrier plate assembly 18, which is positionedinternally of the chamber just inside the chamber entrance 23 associatedwith load lock 12, with plate assembly 18 generally parallel to wall 32and the pressure plate 16, positioned within the chamber rearwardly ofplate assembly 18. Wafer 15 is loaded and held within the load lock andwithin the plate assembly by means which will be described below. Thecontrolled subatmospheric environment which may be provided withinchamber 10 for certain wafer processing operations may be, for example,up to 20 microns of argon or other inert gas for sputter coatingoperations. Because of this evacuated environment, the load lock regionmust be sealed off from the remainder of the chamber interior wheneverdoor 22 is open in order to preserve the evacuated environment. Pressureplate 16 serves the function of isolating the load lock area from thechamber interior (and also several other functions simultaneously atother work stations, as will be shown below). Pneumatic rams 30 and 31,mounted to the rear plate of the processing chamber, drive the pressureplate and carrier plate assembly against front chamber wall 32, withpneumatic ram 30 being applied particularly to the pressure plateconcentrically with load lock arrangement 12 to effect the sealing ofthe load lock. Both pressure plate 16 and chamber front wall 32 areequipped with O-rings 38 arranged in a circular pattern concentric withchamber entrance 23 which provide vacuum seals in the sandwicharrangement of elements defining the load lock. Chamber door assembly22, which in its closed position seals against the outside surface ofchamber front wall 32 and also includes a concentric O-ring 39 toprovide the vacuum seal, completes the load lock by sealing off thechamber entrance 23 from the outside atmosphere. FIGS. 4 and 6 show thecompleted load lock, with pressure plate 16 in its forward, advancedposition, compressing plate assembly 18 against chamber wall 32, andsealing off aperture 37; and door 22 closed to seal off chamber entrance23 to form the load lock about aperture 37, which is only of a size nolarger than necessary to accommodate a single wafer. It may be seen thatan unusually thin low-volume load lock is thereby defined with a minimumof elements, and of a minimum size necessary to accommodate wafer 15therewithin. For further details of the load lock arrangement, see thecommonly owned U.S. Pat. No. 4,311,427 "Wafer Transfer System". FIG. 5shows pressure plate 16 in its withdrawn, rest position, and with thewafer already secured within plate assembly 18 within the chamber.

Cooperating with this thin load lock arrangement is wafer carrier plateassembly 18, which includes a plurality of circular apertures such as at37 (as best seen in FIG. 2) matching the number and spacing of workstations within chamber 10. The apertures 37 are of a diameter largerthan the wafers, are equally spaced from each other, and centered at thesame radial distance from the central axis of the processing chamber.The aforementioned work stations are likewise spaced, so that when anyaperture of the wafer carrier plate assembly 18 is aligned with any workstation of the processing chamber, the remaining apertures are eachsimilarly aligned with a respective one of the remaining work stations.Thus, if a wafer is secured within each of the apertures of carrierplate assembly 18, each of such wafers can be individually processed ata work station simultaneously with the processing of other wafersrespectively at the remaining work stations. In this manner, a wafer isindividually processed at a given station, yet during the same time,several other wafers may also undergo other operations at the remainingwork stations. In particular, while a wafer is being unloaded and/orloaded at load lock 12, another wafer may be coated at coating station14, while still another wafer may be heated at heating station 28.Carrier plate drive 35 intermittently operates to move plate assembly 18by the distance of one station so as to serially present each of thewafers in turn to each of the processing stations in a counterclockwisedirection, until a given wafer finally returns to the load lock forunloading therefrom.

As the wafer is transported from work station to work station as abovedescribed, it is important that the wafer be supported within carrierplate assembly 18 so as to avoid any risk of mechanical damage andabrasion due to being moved about, and generally so as to be protectedfrom mechanical shock, vibration, and abrasion. To this end, wafercarrier aperture 37 is of a diameter such that both a wafer and a set ofclip assemblies 20 can be accommodated within the periphery of theaperture, and recessed and parallel with the carrier plate, therebyprotecting the wafer. The set of thin edgewise-acting clip assembliesalso is important to the formation of the thin load lock arrangement 12,and edgewise resiliently supports the wafer in an upright positionwithin plate assembly 18. An especially advantageous form of such anedgewise acting clip assembly is shown in cross section in FIGS. 4through 8, and is disclosed in detail in the aforementioned commonlyassigned U.S. Pat. No. 4,305,731 "Wafer Support Assembly." A set of fourclip assemblies 20 is mounted within retaining rings 41 which areremovably attached to the disc-like circular wafer carrier plate 42concentrically with each of plate apertures 37, thus forming thecomplete wafer carrier plate assembly 18. This arrangement mounts a setof clip assemblies 20 in spaced relationship within the periphery ofeach circular aperture 37. Retaining rings 41 are of U-shaped crosssection, with each having flanges 46 and 47 defining the inner and outerperipheries thereof, and clip assemblies 20 are recessed within theseflanges. Although it is preferred that four clip assemblies be usedwithin an aperture 37, it is possible to use three, or a number greaterthan four. However, a set of four has been found to provide greaterreliability than three.

As may be seen in any of the FIGS. 3 through 8, clip assemblies 20 eachinclude a block 50 of generally rectangular cross section, which may beof insulating material for applications such as sputter etch for whichelectrical isolation of the wafer is desired, and an elongated springclip 53 firmly engaged in wraparound fashion about block 50. Each clip53 includes at the end thereof opposite the block an arcuate fingerportion or tip 55, which is of a curvature in radius appropriate togripping an edge of a wafer. Extending from block 50 is proximal flatportion 56, which lies within a plane closely adjacent and parallel withthe plane defined by plate aperture 37. On the other hand, distalportion 57 is angled away from portion 56 down toward the plane of plateaperture 37, and defines an obtuse angle with portion 56. This cliparrangement results in a plurality of arcuate tips 55 lying on acircular pattern of diameter somewhat less than that of a typical wafer15 (such circular pattern also lies within the plane of wafer carrierplate 42).

Wafer insertion into load lock 12 may be effected manually by simplypushing a wafer by its edge or rear face into clip assemblies 20. Thiswill, however, involve some edge rubbing of the wafer against distalportion 56, to spread apart the clips somewhat to accept the waferwithin tips 55. In order to insert a wafer without such rubbing contacttherewith, the clips must first be slightly spread, and then allowed torebound against the edge of the wafer upon insertion thereof into theload lock. Although both wafer insertion and clip spreading may be donemanually, it is far preferable to avoid all such manual operations, andthe consequent added risk of damage, error, and contamination associatedtherewith. Chamber door assembly 22 carries thereon a vacuum chuck 60centrally axially therethrough, and a plurality of clip actuating means62 near the periphery thereof. These elements, along with wafer cassetteload/unload assembly 24, provide an automated wafer loading andunloading arrangement for load lock 12 which avoids all such manualhandling of the wafers, and automates the loading process.

As thus seen in FIGS. 1 and 3, chamber door assembly 22 is attached tofront wall 32 of chamber 10 by a heavy-duty hinge 63 having a verticalaxis, to allow the door to open and close in a conventional manner to afully open position as shown, wherein the door and its inside face 64are vertical and perpendicular to the plane of chamber entrance 23, aswell as to plate assembly 18. As shown in FIG. 1, door assembly 22 ismoved between its open and closed positions by means of a conventionalpush-pull actuator 196, and pivot linkage 197 which is attached to hinge63 for causing rotation of the hinge and door. Vacuum chuck 60, whichextends axially and centrally through the door so that the active endthereof forms part of the inside face 64 of the door, engages a waferpresented vertically to the inside face of the door and holds the waferby vacuum suction as the door is closed, whereupon the vacuum chuckaxially extends from the inner door face as shown in FIG. 4 to carry thewafer into engagement with clip assemblies 20. The vacuum chuck willthen withdraw, and wafer 15 is held in the chamber by the clipassemblies and undergoes processing, and movement to the various workstations in turn by rotation of plate assembly 18. The above-describedaxial movement of chuck 60 relative to the door face 64 is accomplishedby means of a conventional pneumatic cylinder 61. In this preferredembodiment, the vertical presentation of the wafer to the inside face 64of the door is effected by load/unload assembly 24, as will be furtherdetailed below.

It should be noted that the load lock arrangement, wafer carrier plateassembly 18, and door assembly 22 need not be limited to a verticalorientation, although this is preferred to help obviate any possibilityof debris settling upon a surface of the wafer. The clip assembly,carrier plate and load lock arrangement of the invention, as well as allof the work stations, function equally well if oriented horizontally.Indeed, although the load/unload assembly 24 for the vertically-orientedwafer cassettes is meant for vertical operation, the door assembly 22could easily be made to load wafers into the load lock in a horizontalplane, yet accept wafers in a vertical orientation, by suitablemodification of its manner of mounting to the chamber wall in aconventional manner.

As noted above, it is preferable to avoid simply loading a wafer intothe clip assemblies 20 within the load lock by pushing a wafer againstthe angled distal portion 57 of the clips. In order to insert a waferwithout such rubbing contact, the clips must first be slightly spread,and then allowed to rebound against the edge of the wafer upon insertionthereof into the load lock. This is accomplished automatically as thewafer is being inserted by vacuum chuck 60 by four clip actuating means62 mounted within the door as aforementioned. Each clip actuating means62 is mounted so as to be in registration with a corresponding one ofclip assemblies 20 when the door is in its closed position. Each clipactuating means 62, shown in detail toward the lower end in FIG. 4,includes a pneumatic cylinder 65, and a contact pin 66 which movesaxially inwardly and outwardly and is propelled by cylinder 65. Pins 66are each in registration with one of flat proximal clip portions 56 whenthe door is in its closed position. With door 22 closed, pins 66 areextended just prior to insertion of a wafer; or as a wafer is to bewithdrawn. The pressure of a pin 66 against the facing flat clipproximal portion 56 presses the clip and causes the tip 55 to swing backand outwardly, thereby releasing the clips, to facilitate insertion orremoval of a wafer without rubbing contact therewith.

During wafer unloading after completion of the wafer processing, theseoperations are reversed, with the chuck again extending and applyingvacuum to the backside of the wafer to engage same, with the clipactuating means again cooperating to release the clips, whereupon thedoor opens and the chuck retains the wafer on the inside A stepper motormeans 80 is provided as the driving power for the chain means 75, toprovide precise control over the movement of the cassettes, so that anychosen individual wafer within a cassette may be positioned forinteraction with the wafer elevator assembly 68. A conventional memorymeans is coupled to stepper motor 80 and wafer elevator assembly 68,which stores the location of an individual wafer within a cassette.Thus, although several further wafers may have been loaded intoprocessing chamber 10 and the cassette accordingly advanced severalpositions since a first wafer was loaded, yet upon emergence of thecompleted first wafer, the stepper motor may be reversed the requirednumber of steps to return the completed wafer to its original position,then again resume its advanced position to continue its loadingfunction.

The cassettes 70 hold a plurality of the wafers 15 in spaced, facing,aligned and parallel relationship, and are open at the top as well asover a substantial portion of their bottom, to permit access from belowand above the wafers. They must be loaded so that the front faces of thewafers, which contain the grooves, steps, and other features definingthe microcircuit components, face away from the inside face 64 of theopen door 22, and so that the rear faces of the wafers face toward thedoor assembly. This ensures that when the vacuum chuck 60 engages thewafer, no contact is made with the front face containing the delicatemicrocircuits, and that the wafer is properly positioned upon insertioninto the load lock 12 so that it will be oriented properly with respectto processing equipment within the processing chamber 10.

The wafer elevator assembly 68 is positioned below and just to the leftside of chamber entrance 23 and includes an upper guide plate 82, ablade-like elevator member 83, and an actuating cylinder 84 connectingto the lower end of member 83. Elevator blade member 83 is guided formovement up and down in a vertical path intersecting at right anglesconveyor 69 between rails 72 and 73 to inside face 64 of door 22. Guideslot 85 in guide plate 82 just below the inside face of the door in theopen position provides the uppermost guide for blade 83, while avertical guide member 86 extending below the conveyor toward theactuating cylinder also aids in retaining blade 83 on its vertical path.The width of blade 83 is less than that of the spacing between rails 72and 73, ad also less than the spacing between the main walls of thecassettes 70 which straddle rails 72 and 73. Blade 83 is also thinnerthan the spacing between adjacent wafers retained in cassettes 70.

Blade member 83 is further provided with an arcuate upper end 87 shapedto match the curvature of the wafers, and a groove within this endadapted to match the thickness of a wafer and retain a wafer edgewisetherewithin. Thus, elevator blade member 83 passes between guide rails72 and 73 and intersects conveyor and cassette at right angles thereto,upon stepper motor means 80 and chain drive 75 bringing a cassette andwafer into registration over the path of the blade. As may be seen, thecassettes are constructed to allow access from below to the wafers, andto allow elevator blade 83 to pass completely therethrough. Accordingly,upon stepper motor means 80 and chain means 75 placing a cassette andwafer in registration over the path of the blade, blade 83 movesupwardly between the conveyor rails to engage from below a wafer withinthe groove of its upper end 87, and elevate the wafer upwardly to aposition in registration concentrically with and immediately adjacentinside face 64 of chamber door 22 in its open position. Note that sincethe wafers are vertically oriented, gravity aids in holding the wafersfirmly yet gently and securely in the grooved end 87 of the blade.Contact with the delicate front face of the wafer, upon which thedelicate microcircuits are defined, is therefore virtually completelyavoided, unlike the case of typical automated handling when the wafer isin a horizontal orientation. Thus the risk of damage or abrasion to thewafer is greatly lessened.

Upon arrival of the wafer at the door 22, vacuum chuck 60 engages wafer15 at its rear face by suction, and elevator blade 83 then is loweredthrough guide slot 85 and the cassette to a point below conveyor 69.Door 22 then closes with the wafer retained by the chuck 60, and thewafer is thereby loaded into the load lock arrangement 12 and chamberentrance 23 sealed simultaneously as described above for processingwithin chamber 10. Prior to completion of processing for wafer 15, stillfurther wafers may be loaded within the remaining ones of apertures 37of plate assembly 18; therefore the stepper motor and chain drive stepthe cassette one wafer position to move the next wafer serially inposition over blade 83. Blade 83 then rises to repeat its operation ofmoving this next wafer upwardly to the open door, whose vacuum chuckthen again engages that wafer for insertion into the load lock.Meanwhile, upon completion of processing for original wafer 15 byrotation in turn to each station, it is again at load lock 12, andvacuum chuck 60 again extends to the backside of the wafer while thedoor is still in its closed position, and clip actuating means 62simultaneously depress the clips to disengage same from the wafer toenable the removal thereof by chuck 60, whereupon the door is opened andthe wafer again positioned over the path of blade 83. Meanwhile, steppermotor means 80 and chain means 75 move the cassette back so that theoriginal position of wafer 15 is presented over the blade path. Blade 83then rises through conveyor rails 72 and 73 and slot 85 upwardly toengage the lower edge of wafer 15, whereupon chuck 60 releases thewafer, and enables blade 83 to lower the wafer back into its originalposition within the cassette. The cassette is then propelled forward tothe position of the next wafer to be processed serially.

Prior to the elevation of the individual wafers by the elevator assembly69 and loading into the load lock, it is desirable to insure a standardorientation for the wafers, so that the usual guide flat 91 across acord of each wafer is aligned to be lowermost in the cassettes. In thismanner, each of the wafers is assured of assuming the same position withrespect to the processing equipment within the chamber. Further, makingcertain that the guide flat is in a given predetermined position assuresthat clip assemblies 20 within plate assembly 18 will function properly,and not accidently engage a flat of the wafer instead of a portion ofthe main circular edge. To ensure such standard orientation, a pair ofopposed rollers 90 is provided which are longitudinally extended alongand between rails 72 and 73 so that the roller axes are parallel withthe rails. The rails are positioned in the path of the cassettes justprior to the position of the elevator assembly 68, so that orientationof the wafers is completed prior to their reaching the elevatorassembly. Upon passage of the cassette over the rollers, the rollers areelevated and then are driven serially and in opposed senses, oneclockwise and the other counterclockwise, and lightly contact thecircular edge of the wafers. Contact with moving rollers 90 then has theeffect of rotating the wafers within the cassettes until the guide flat91 of each wafer is positioned at a tangent to the moving rollers,whereupon contact with the roller is lost and the wafers are allpositioned with guide flats facing downwardly and in alignment,whereupon the rollers 90 are retracted downwardly.

As aforementioned, pressure plate 16 is driven against carrier plate 42and wall 32 whenever door 22 is in its opened position, to protect theevacuated interior environment of the chamber from the atmosphere. Wehave seen that FIGS. 4 and 5 show in more detail the relativepositioning of the pressure plate and wafer carrier plate, with FIG. 4showing the aforementioned sandwich arrangement of the elements definingthe load lock arrangement 12, and FIG. 5 showing the relativepositioning of the elements when the pressure plate is in its withdrawnposition. Note also that FIG. 4 shows vacuum chuck 60 in its extendedposition as the wafer is inserted into clip assemblies 20 with pins 66of clip actuating means 62 partially extended after having spread theclips; while in FIG. 5, the vacuum chuck has withdrawn, as have the pinsof the clip actuating means, and the wafer is now securely mounted inwafer carrier plate assembly 18. With pressure plate 16 withdrawn, thewafer is now ready to be rotated to subsequent processing stations. InFIG. 6, the vacuum chuck is also in the withdrawn position; however, thevacuum suction is operative, and the wafer is shown in its positionagainst the inner face 64 of chamber door 22. This is, of course, theposition of the elements of the load lock and the wafer just after thewafer has been withdrawn from clip assemblies 20, prior to its beingremoved from the load lock; or, it also represents the position of theelements just after the door has been closed and the vacuum chuck hasnot yet advanced the wafer to its position within aperture 37 of thewafer carrier assembly. Pins 66 of the clip actuating means 62 are shownbearing upon the clips just prior to depressing same to spread the clipsin order to accept the wafer therewithin.

Upon completion of loading of the load lock with a wafer 15, the loadlock is rough-pumped during a cycle lasting much less than a minute downto a level which, though still a good degree less evacuated than thechamber, does not appreciably disturb the chamber environment when thepressure plate is withdrawn as shown in FIG. 5, and the wafer 15 rotatedto the next work station. This may be effectively done in such a shorttime frame not only because the load lock is of such small volumecompared to the chamber (being only essentially that required to containthe wafer itself), but also because the outgassing load which wasintroduced therein is essentially only that of the wafer surfacesthemselves, since no ancillary support equipment is utilized fromsources outside of the load lock region, and since in any event the areaof the clip assemblies supporting the wafer within the chamber is smallrelative to the wafer. This should be contrasted with the situation ofprior art systems in which platens and other outside supports areintroduced into the load lock, which supports have considerable areawhich contributes very greatly to the gas pumpdown load. Of course, thelack of such supports introduced from the outside also contributessignificantly to a lessened risk of contamination. It should also benoted that the situation gets even better as the wafer advances to thesubsequent work stations, since that portion of the pressure plate atthe load lock region which is exposed to atmosphere (or the loadingenvironment, which preferably is enclosed in a dry nitrogen environment)does not rotate with the wafer, but rather remains in the same loadingstation location, away from the remaining work stations and moreover issealed off from the chamber environment during deposition.

While a wafer is being loaded into and/or unloaded from load lockstation 12, pressure plate 16 is in its active advanced position of FIG.4, whereby plate assembly 18 is forced against front wall 32 of thechamber, the pressure plate is similarly urging wafers in the remainingstations into contact, or closer working cooperation, with theprocessing devices at those stations having processing devices on frontwall 32. For example, at wafer heating station 28, the next stationbeyond load lock station 12, wafer heating means 92 for promoting waferoutgassing is provided. The wafer heating means 92, which is shown inFIG. 7, comprises a cylindrical supporting member 93 of somewhat lesserdiameter than the wafers and includes as the heating element 94 aceramic disc in which resistance wire is imbedded in a manner to allowthe surface of the ceramic disc to be heated controllably and to agenerally uniform temperature over its planar surface. The wafer heatingmeans 92 is mounted upon front wall 32 of the processing chamber in asealed aperture thereof, such that the heated surface of the elementprotrudes from the plane of the chamber front wall 32 to a slightdegree. When pressure plate 16 is in its relaxed state, the location ofthe pressure plate with respect to the front wall of the chamber isspaced sufficiently so that the heated surface is not very close to thecarrier plate or any wafer therewithin. However, when pressure plate 16is in its active forward position, the wafer carrier plate 42 iscompressed against front wall 32 of the chamber so that the spacingbetween the heated surface and any wafer in registration with theheating station is very close, but not so close so as to contact theheated surface, as may be seen from FIG. 7.

In a vacuum environment, the principal mechanism of heat transfer is byradiation. P-doped silicon wafers, which are widely used insemiconductor device fabrication, are quite transparent to infraredradiation. As a result, the rates of wafer temperature rise are too lowto be effective in promoting increased wafer outgassing rates during theshort outgassing cycle required in the apparatus of this invention.Because the wafers are stationary while at the wafer heating station 28,it is convenient to increase the rate of transfer of heat from theheating element 94 to wafer 15 by utilizing gas conduction heattransfer. This is accomplished by introducing through the central pipe114 as shown in FIG. 7 some fraction of the argon gas employed foroperation of the sputter deposition source directly into the spacebetween heating element 94 and wafer 15. Heat transfer is effected as aresult of argon atoms striking hot and cold surfaces alternately. Toachieve desirably high rates of heat transfer, it is necessary tointroduce the argon into heating station 28 at pressures which are inthe range approximately 100 to 1000 microns, which are one to two ordersof magnitude greater than the normal argon pressure in the main chamberof about 10 microns.

Wafer heating member 92 comprises also a backing plate 98 to whichcylindrical support member 93 is attached. A vacuum seal between backingplate 98 and chamber wall 32 is provided by O-ring 115. To avoiddegradation of the vacuum sealing properties of O-ring 115 byoverheating as a result of heat generated in heating element 94,conduits 96 and 97 passing into and through backing plate 98 areprovided to allow coolant to be flowed into and out of the backingplate, thereby cooling backing plate 98 to maintain the vacuum integrityof O-ring seal 115.

In certain applications, it will be desirable to heat and clean thewafers at the heating station by means of rf (radio frequency) sputteretch using methods which are well known to those skilled in the art. Inorder to perform the rf sputter etch operation in the short cycle timerequired in the apparatus of this invention, the required application ofrf power may cause the wafer temperature to rise to an undesirable orunacceptable level. This problem may be alleviated through the use ofgas conduction heat transfer once again, this time to transfer heat fromthe wafer to a cooled heat sink.

A suitable wafer cooling means 118, which is shown in FIG. 8, comprisesa cylindrical heat sink member 119 mounted on a backing plate 120. Avacuum seal between backing plate 120 and chamber wall 32 is provided byO-ring seal 121. To maintain the temperature of heat sink 119 at asuitably low value, conduits 128 and 129 passing through backing plate120 and into and through heat sink 119 are provided to allow coolant tobe flowed into and out of heat sink 119, thereby maintaining itstemperature at the desired level. Heat sink member 119 has a planarsurface 125 closely spaced to but not in contact with wafer 15 whenpressure plate 16 is in its active forward position. A central pipe 126as shown in FIG. 8 is provided to allow some fraction of the argon gasemployed for operation of the sputter deposition source to be introduceddirectly into the space between heat sink 119 and wafer 15. Suchintroduction of argon gas increases the rate of cooling by increasingthe rate of heat transfer from wafer 15 to heat sink 119, in the samemanner that the rate of heat transfer was increased from heating element94 to wafer 15 in the case of heating station 28, as described earlierin connection with FIG. 7.

The next station to which the wafer is advanced is coating station 14,which is mounted on the back plate 99 of the chamber, and for which anaperture 101 of circular form is made within the pressure plate, toenable the sputtering source to direct coating therethrough to a waferadvanced by carrier plate assembly 18 into registration at the coatingstation. A shutter 102 is also provided to enable the coating materialto be blocked during rotation of the carrier plate assembly and when awafer is not present at the coating station. FIG. 9 shows therelationship of the elements at the coating station 14 in more detail.It might be noted that the geometry of FIG. 9 depicts the elements intheir configuration just prior to movement by the pressure plate to itsactive forward position, to compress the wafer carrier plate againstfront wall 32 of the chamber. Thus the position of the wafer duringcoating will be closer to the front wall than illustrated in the restposition of FIG. 9, such that wafer 15 will be held in stable andstationary fixed concentric relationship with sputter source 100.

A major advantage of the manner of supporting the wafer edgewise andindividually coating same is now clear. It is well known that thesputtering process whereby a metallization coating is deposited onto thefront side of the wafer will cause the wafer to further be heated, andthus increase outgassing of the wafer at the worst possible time.However, the close coupling between the source 100 and wafer 15 with theconsequently rapid coating deposition rate (approximately 10,000angstroms per minute); the low level of contaminants (due, for example,to the lack of external wafer supports and the lack of any adjacentwafers adding outgassing products to the environment immediately aheadof the front face of the wafer); and the fact that the back-sideoutgassing products will most likely impinge on the shield structuressurrounding the sputtering source; all contribute to a much lowerconcentration of contaminants due to outgassing ending up on the frontsurface of the wafer, compared to prior configurations. In the case ofearlier batch and other load lock systems, a plurality of wafers areadjacent each other, will likely be supported upon a platen, and willnot have the benefit of a source-to-wafer geometry to allow forindividual shields upon which contamination products and coatingmaterial could preferentially combine rather than on the wafer surfaceitself, as in the present configuration.

Still other advantages grow out of the fact that the metallization ofthe individual wafer is carried out with the wafer in a verticalorientation, and further, that the metallization is done while the waferis stationary. It is clear that if any debris or particulate matter ispresent in the system, the chances of such matter coming to rest on avertical wafer surface are much reduced as compared to a case whereinthe wafer is horizontally oriented. The fact that all motion within thechamber ceases during metallization means that no mechanical motion,shock, or vibration is present which would tend to promote debrisgeneration, as, for example, by dislodgment of stray metallizationmaterial from wafer support structures, shields and other such surfaces.Additionally, in the present system, the stress on any such straycoating build-up on shields, and other internal chamber structure isfurther alleviated by lack of repeated exposure to air, a lessening ofmechanical strains due to the necessity for stopping movement during theprocessing period, and fewer moving parts. The very small structure ofclip assemblies 20 which support the wafer is not even itself exposed toair during normal operations, since the load lock is normally operatedin a dry nitrogen environment, rather than moisture-bearing air.

The close-coupled wafer-source relationship, and its stationary aspect,have additional favorable implications for the desirable characteristicsand homogeneity of the films deposited. The local rate of deposition ata point on the wafer surface depends on the radial position and surfacetopography, i.e., whether the surface at that position is planar, or thesidewall or bottom of a step or groove, or the inward or outwardorientation of the sidewall, as will be discussed further below. Becausethe wafer is stationary with respect to the source, deposition at eachpoint proceeds at a constant rate, rather than at a time-varying ratethroughout the deposition (assuming constant power applied to thedeposition source.) Thus, deposition thickness at various points andtopographies will be radially symmetric about the axis common to theconcentrically located deposition source and wafer.

Further, as implied above, contamination levels incorporated into thecoating depend on the relative arrival rates at the wafer surface ofmolecules of contaminant background gases (such as oxygen) and atoms ofthe sputtered coating material (such as aluminum). If the partialpressures of contaminant background gases remain constant duringconstant-rate deposition, then the local contaminant level incorporatedinto the coating will be homogenous throughout the thickness of thedeposited film.

By contrast, this situation has not obtained in prior art load locksystems in which wafer motion relative to the source leads to depositionrates which vary with time during the deposition period. This then leadsto inhomogeneities in contaminant level incorporated into the coatingduring film growth, which in turn has adversely affected the yields ofgood semiconductor devices from the wafer. In the case of prior artsystems in which wafers make multiple passes past the deposition source,the metal film is deposited in layered fashion, which in turn leads toan undesirable layered contaminant level profile.

Reverting now to a more detailed consideration of sputtering source 100of FIG. 9, we see that the emitting end thereof includes a ring-shapedtarget 112, which is shown schematically in dotted representation inFIG. 9, but which is shown in greater detail in cross-section in theschematisized cross-section of FIG. 10. An example of such a sputteringsource may be found described in more detail in U.S. Pat. No. 4,100,055,issued Jul. 11, 1978 to R. M. Rainey for "Target Profile for SputteringAppparatus". Such a sputtering source is also commercially availablefrom and manufactured by Varian Associates, Inc. under the registeredtrademark "S-Gun". Such sputter coating sources employ a magneticallyconfined gas discharge and require a subatmospheric inert gasenvironment as of argon. Other sputtering sources with ring-shapedtargets may also be used, as, for example, a planar magnetron source.

Positive ions from the gas discharge strike S-Gun target 112, which ismade of the source material for coating which is desired to bedeposited, for example, aluminum. Thus, source material is caused to besputtered from the target outwardly from the source. The sputter coatingprocess is carried out in the subatmospheric controlled environment ofvacuum chamber 10, within which the dominant gas is normally argon,deliberately introduced at very low pressures to sustain the gasdischarge. The argon pressure required to sustain the discharge isgenerally in the range 2-20 microns, and has been found to influencecoating quality, as will be further described below It is found that theargon needed for such discharge sustenance may advantageously come fromthe argon deliberately introduced at the various wafer processingstations, as described above in connection with wafer heating station 28and wafer cooling means 118.

As may be seen from FIGS. 9 and 10, source 100 may be regarded as aring-shaped source with an inner diameter and an outer diameter, andwith a profile connecting the two diameters of generally invertedconical configuration averaging about 30 degrees. It will be noted thatthe term "conical" is an approximation, since in practice the profile oftarget 112 will erode significantly over the life of the target. FIG. 10illustrates in superimposed fashion both a typical new target profile,and that same target's profile at the end of target life. Moreover, manyprofile variations are possible; see, for example, the above mentionedU.S. Pat. No. 4,100,055; further, some useful ring sources, for example,of the planar magnetron type, will not exhibit this generally conicalprofile.

Despite such erosion, a significant fraction of the material emanatingfrom target 112 is still directed inwardly toward the axis of thesource, even when near the end of target life. In addition, somematerial from the more eroded bottom sections of the target which may bedirected outwardly will actually be intercepted by the eroded sides,from which resputtering in a generally inwardly direction may occur.Thus, even with target erosion, the source 100 may be characterized asacting as a ring-shaped source, and of effectively generally invertedconical configuration. It is believed that the generally invertedconical configuration leads to a greater efficiency of utilization ofmaterial sputtered from the source than for a planar configuration. Thisis believed to be so because a larger fraction of the sputtered materialis directed generally inwardly because of the conical configuration,resulting in a larger fraction being deposited on the wafer instead ofbeing deposited uselessly on the shielding.

As may be seen from FIG. 9, the wafer 15 is held in fixed concentricstationary and parallel relationship with respect to source 100 duringcoating as described above, being supported resiliently within therelatively thin wafer carrier or transfer plate assembly 18 by clipassemblies 20. These relationships are more analytically treated in theschematic showing of FIG. 10, which serves to help define the effectivesource target-to-wafer spacing x, the effective source diameter D_(s),and the radial position r along the wafer to be coated measured from thecenter thereof. In defining these quanities, it is useful to identify aneffective plane of the source P_(s), which is the planar level such thatby the end of target life, the amounts of material eroded above andbelow this planar level are equal. It is also useful to define theeffective source diameter D_(s) as that diameter such that by the end oftarget life, the amount of material eroded outside of that diameter isequal to the amount of material eroded away inside that diameter.Accordingly, x is analytically the distance between the wafer and theplane P_(s). A typical sputtering source 100 such as is commerciallyavailable can have actual outer and inner target diameters of 5.15inches and 2.12 inches respectively, and a target height of 0.88 inches,as shown in FIG. 10. Thus, for the erosion pattern shown, the effectivesource diameter D_(s) is approximately 4.6 inches for such a commercialsource. Likewise, it can be seen that the effective plane P_(s) of thesource is located approximately 0.5 inches below the top edge of theuneroded target.

It has been found that, surprisingly, coating of the semiconductorwafers with very good planar uniformity and superior step coverage ispossible while maintaining wafer 15 stationary as shown with respect tosource 100 during deposition, and that this may be done withinrelatively short deposition times of approximately one minute, as longas certain geometrical and positional constraints are observed, and aproper inert gas environment and pressure are maintained. Thesepreconditions for obtaining very good uniformity and superior stepcoverage, as well as the degree of improvement in these factors whichmay be expected, are illustrated graphically in FIGS. 11 through 15. Itshould be understood that the term "uniformity" as utilized herein andin the Figures is the ratio of thickness at the radial position at whichthe uniformity is being considered to the thickness at the center of thewafer. Thus, as usual, uniformity is normalized to unity at the centerof the wafer.

FIGS. 11 and 12 illustrate uniformity of thickness of deposition on themain uppermost planar surfaces of wafer 15 as a function of radialposition r in inches, with uniformity being a relative measure,normalized as aforementioned. In FIG. 11, four curves are shown, eachbeing associated respectively with source-to-wafer distances x of 2, 3,4 and 5 inches. The argon environment of the chamber is at a pressure of3 microns. In FIG. 12, both uniformity curves are for source-to-waferdistance x equal 4 inches; however, one is for an argon environment of 2microns pressure, while the other is for an argon environment of 10microns pressure.

FIG. 11 illustrates the surprising result that uniformity of depositionover the planar surface of wafer 15 is very good, even with no relativemotion between source and wafer, as long as the effective sourcediameter D_(s) is greater than the diameter D_(w) of the wafer. Morespecifically, as shown by FIG. 11, the uniformity of planar coverage isbetter than ±15% as long as: (a) x is approximately within the range 0.4D_(s) to 1.1 D_(s) (x=2-5" for D_(s) =4.6"); and (b) the maximum waferdiameter D_(wmax) is less than approximately 0.9 D_(s), (or a value ofr, equal to 1/2 the wafer diameter, of approximately 2.1" for a sourceof D_(s) =4.6" effective diameter).

Even better tolerances are exhibited over certain ranges of waferdiameters within the above outside limits. For example, over the rangeof ratios of wafer diameter-to-source diameter up to about 0.65 (or atradial positions r up to about 1.5"), uniformity is better than ±8%. Inother words, over a wafer diameter of 3.0", and with a source effectivediameter of 4.6", and assuming 3 micron argon pressure environment, theplanar uniformity is better than ±8%, regardless of whichsource-to-wafer spacing x is chosen within the range 0.4 D_(s) to 1.1D_(s). By restricting the source-to-wafer spacing x to the rangeapproximately 0.4 D_(s) to 0.9 D_(s) (x=2-4" for D_(s) =4.6"), theplanar uniformity is further improved to better than ±5%, as may be seenfrom FIG. 11.

The foregoing planar uniformity figures will be influenced by the argonpressure of the environment within which the deposition is carried out,but the above surprising uniformity results hold nonetheless.Considering the influence of the pressure factor more particularly, FIG.12 shows what occurs for the exemplary case of source-to-wafer distanceof x=4" and a 5" outer-diameter source (for which the effective sourcediameter D_(s) =4.6") under two conditions a 2-micron pressure argonenvironment, and a 10-micron pressure argon environment. We see that atan argon pressure of 2 microns, a uniformity of ±10% is obtained out toa maximum wafer diameter of approximately 4.3" (radial position r ofapproximately 2.2"). Upon raising the argon pressure to 10 microns, themaximum diameter to maintain the same uniformity of ±10% is reduced byabout 16% to approximately 3.6" (radial position of approximately 1.8").Alternatively, it can be seen that for a wafer of 3.0" diameter, theuniformity is about ±4% for an argon pressure of 2 microns, and becomesapproximately ±7% for an argon pressure of 10 microns, both of which aresuperior results for many semiconductor wafer applications.

FIG. 15 is a further showing of the influence of the pressure of theargon environment. In this Figure, for a source-to-wafer spacing of 4",uniformity of planar coverage is shown as a function of microns of argonpressure for two radial positions, one at 1.5", and the other at 2.0".As expected, the innermost radial position will exhibit the highestuniformity, but both vary in similar fashion over the range of argonpressures. It will be seen that from 0 to 5 microns, the change is mostrapid at both radial positions However, from about 5 to 15 microns,uniformity changes very little, on the order of a few percent in bothcases. Thus, it may be seen that the planar uniformity is not verysensitive to changes in argon pressure within the range 5 to 15 microns,a surprising fact which becomes important in optimizing step coverage,which is much more affected by changes in argon pressure, as will beexplained in more detail below.

In order to obtain a fully satisfactory coating, it is essential thatthe sidewalls of such features as grooves and steps within the mainplanar surface of wafer 15 be adequately coated, i e., that good "stepcoverage" be provided. Sidewalls may be defined as those surfacesgenerally perpendicular to the main planar surface of the wafer. Stepcoverage is difficult both to specify and to measure. Scanning electronmicroscopes are used by semiconductor device manufacturers as aprincipal tool for assessing at least subjectively the adequacy of stepcoverage achieved in particular applications.

In the prior art, extensive experience taught the need for relativemotion of the wafers with respect to the deposition source to obtainadequate uniformity and step coverage, as we have seen. A recent articleby I. A. Blech, D. B. Fraser, and S. E. Haszko, "Optimization of A1 stepcoverage through computer simulation and electron microscopy", J. Vac.Sci. Technol. 15, 13-19 (January-February 1978), reports excellentagreement between computer simulations of metal film deposition andscanning electron microscope (SEM) photographs of actual film stepcoverage obtained with an electron beam evaporator source plus planetaryfixture configuration, with deposition onto unheated substrates.Although the source employed in the references is a small-area thermalevaporation source, while in the apparatus of the present invention, aring-shaped sputter source 100 is employed, and further the instantsource is stationary and close-coupled, the geometrical considerationsexamined in the reference are quite indicative. Although, the depositionon various surfaces by a source as in the present invention should bemuch better than from a centrally-located source of small area as in thereference, the considerations examined in the reference neverthelessindicate that for wafer sizes of practical interest relative to thediameter of the ring source, enough shadowing would occur to place thepossibility of adequate step coverage over much of the wafer in seriousdoubt. Surprisingly, however, in the present invention, very highquality step coverage is, in fact, achieved. Although many of theconfigurations above described in connection with FIGS. 11 and 12 whichresult in very good uniformity of planar coverage also afford good stepcoverage, certain ranges and values of source-to-wafer spacing andwafer-to-source diameter relationships have been identified whichprovide still better quality in such coverage as have certain ranges andvalues of argon pressure for the coating environment.

FIGS. 13 and 14 aid in defining these optimal parameters, and plot themeasurements of thickness of sidewall coverage as a function of radialposition r. All data at each radial position are normalized to thethickness of deposition which will be obtained on the planar surface atthat radial position. Note that the horizontal axis of each graph showsvalues extending to both sides of the vertical axis. This is because,physically, a given groove defined in the wafer may have sidewalls whichface both toward the center of the wafer and away from the center of thewafer. Not surprisingly, the outwardly-facing side generally receives asignificantly thinner deposit than the side facing in, despite bothbeing generally in the same radial position. This fact is reflected inFIGS. 13 and 14, so that the left side of the horizontal axiscorresponds to radial positions for sidewalls which face outwardly,while the right side corresponds to radial positions for sidewallsfacing inwardly. It will further be noted that the vertical graph plotssidewall coverage as a percentage of the planar surface coverage, and isnormalized as indicated above. Both graphs show a curve for 3 micronsargon pressure and 10 microns argon pressure, with FIG. 13 being for asource-to-substrate distance x of 4", while that of FIG. 14 is for asource-to-substrate distance x of 3".

As is readily apparent from the curves, a further unexpected result isrevealed in that the sidewall coverage on the more difficult to coatoutwardly-facing wall is dramatically improved upon raising the pressureof the argon atmosphere from 3 microns to the 10 micron region. This istrue for a range of source-to-wafer spacings, for example, in both thecase of x=3 and x=4. In the FIG. 14 case (x=3"), sidewall coverage isincreased, for example, from less than 4% to almost 12% at a radialposition of 2.0" (corresponding to the edge of a 4" diameter wafer), andfrom 15% to 20% at the edge of a 3" diameter wafer. From FIG. 13 (x=4"),sidewall coverage is increased from approximately 9% to approximately17% at the edge of a 3" wafer. Again, we see that the same generalsource-to-wafer distances and the same kinds of relationships betweenwafer and source which were found to give rise to good planar coveragealso result in good sidewall coverage, particularly when some care istaken to consider the beneficial effect of increased argon pressure inimproving coverage of the outwardly-inwardly facing sidewall, within arange which does not seriously degrade the uniformity of planar surfacecoverage.

Further, within these general parameters, more specific ranges are ofgreat interest for the most improved sidewall coverage. Morespecifically, for source-to-wafer distances x of 0.4 D_(s) to 0.9 D_(s)(i.e., x=2-4", assuming an effective source diameter D_(s) =4.6"), andwafer diameters within approximately 0.7 D_(s) (or up to D_(w) =3.2",assuming an effective source diameter D_(s) =4.6"), not only will planardeposition uniformity be better than ±10%, but also minimum sidewallcoverage will be at least 10% of the planar coverage, or more, as longas the argon pressure is kept in the vicinity of 10 microns. Certainranges within the foregoing are still more useful. For example, as wehave seen from FIGS. 13 and 14, at a source-to-wafer distance of x=3",sidewall coverage is at least 20% of the planar coverage on out to theedge of a 3" wafer, while at x=4", sidewall coverage is at least 17% inthe same situation.

An exemplary set of results can be tabulated from the above data forargon pressures during coating of 10 microns, and forsource-to-substrate distances x in the range 0.4 D_(s) to 0.9 D_(s), asfollows:

                  TABLE I                                                         ______________________________________                                                               Maximum diameter                                       Uniformity of                                                                             Minimum    of semiconductor                                       planar surface                                                                            sidewall   wafer or other                                         coverage    coverage   substrates (D.sub.wax)                                 ______________________________________                                        Better than ±20%                                                                       --         D.sub.wmax = 4.2" = 0.9 D.sub.s                        Better than ±10%                                                                       Greater    D.sub.wmax = 3.2" = 0.7 D.sub.s                                    than 10%                                                          ______________________________________                                    

Similar results are obtained for 4" and 5" diameter wafers. Thus, forexample, for uniformity better than ±10%, and sidewall coverage greaterthan 10%, the minimum effective source diameters D_(s) are approximatelyequal to 5.7" for 4" diameter wafers, and 7.1" for 5" diameter wafers.It is of course possible to coat 3" and 4" diameter wafer using sourcesdesigned for 5" diameter wafers. In sustained production, however,considerations of efficient utilization of source material may argue infavor of sources whose sizes are optimized to each wafer size.

It is believed that some of the observed improvements in sidewallcoverage with increasing pressure of the argon environment arise as aresult of collisions between the sputtered metal atoms and the atoms ofargon gas located in the space between the source and the wafer.Sputtered atoms are thus "gas scattered" around corners and over edgesinto regions which are shadowed from line-of-sight deposition. SEMphotographs do indeed show that the step coverages obtained using 10microns argon pressure, for example, are significantly better than thoseobtained using an argon pressure of 3 microns.

It is further known (see for example, the paper by Blech, et al.,referenced above) that step coverage can be improved by heating thesubstrates during aluminum deposition to temperatures on the order of300° C. This beneficial result arises from the increased mobility atelevated temperatures of the aluminum atoms during film growth. With theclose-coupled source used in the present apparatus, and the stationarysource-to-wafer relationship during coating, high deposition rates areachieved, and at a rate of 10,000 angstroms per minute, for example,considerable heat is generated. For example, the heat of condensation ofaluminum plus the kinetic energy of the sputtered atoms reaching thewafer surface is approximately 0.2 watts per square centimeter at theabove deposition rate. The resulting temperature rise of a typicalsemiconductor wafer during a one-minute deposition cycle may be as muchas 200° C. Thus, such elevation of wafer temperature during thisclose-coupled and stationary-configuration deposition within the presentapparatus may help cause aluminum migration to occur to a degree whichis beneficial to step coverage. Further, additional application of heatcan improve step coverage even further. However, the possibility ofclosely controlled application of even heat to wafers to be coated inorder to take full advantages of these possibilities has not heretoforebeen feasible. In prior art systems, the wafers are in uncertain thermalcontact with the wafer support structure. Close coupling between waferand source has been the exception, rather than the rule, and depositionrates for a single wafer have not been very high. Control over wafertemperatures during processing has left much to be desired.

By contrast, in the apparatus of the present invention, wafers arehandled on an individual basis. In addition, wafers are held stationarywhile at the various processing stations and are closely coupled thereto(except for the load lock station). Further, since the wafers aresupported edgewise, both sides of the wafers are accessible forprocessing. As one consequence of these features, it has now beenpossible to provide means such as 92 to control wafer temperaturesindividually at each processing station. In particular, temperaturecontrol in the present invention is achieved as aforementioned by thegas conduction heat transfer means discussed above in connection withwafer heating station 28 and wafer cooling means 118. These meansovercome the problems of heating or cooling the wafer in an evacuatedenvironment by introducing some fraction of the argon gas (a certainamount of which is required in any event for operation of the sputterdeposition source) in the space behind the back face of the wafer, asdescribed above. Such wafer heating or cooling means may also beemployed elsewhere, for example, at the coating station itself. It isknown that not only step coverage, but also various film properties,such as reflectivity, resistivity, and contact resistance are affectedby wafer temperatures during processing. To obtain, consistently andreproducibly, a particular set of desired film characteristics requiresthat the wafer temperatures be reproducibly controlled throughout theprocessing cycle. Thus, the apparatus of the present invention providesmeans for obtaining, consistently and reproducibly, a particular set ofdesired film characteristics including step coverage through wafertemperature control throughout the processing cycle.

Referring once again to FIG. 1, the next station to which the wafer 15is advanced is a second coating station 128. In some applications, twodifferent metals are required to be deposited sequentially onto thewafer 15, the first metal being deposited at the first coating station14, and the second metal being deposited at the second coating station128. When only a single metal is employed, the second coating station128 may be left inoperative. Alternatively, coating station 128 may beemployed to double the amount of sputtering source material available,thereby doubling the time between replacement of the ring-shaped targets112. Both coating stations may be operated simultaneously with, forexample, each station operating at one-half the normal deposition rate.Alternatively, of course, one coating station may be operated aloneuntil, for example, the end of target life is reached, whereupon theresponsibility for deposition may e transferred to the other coatingstation.

The next station to which wafer 15 is advanced is the cooling station130. If the wafer temperature is not too high when it reaches thecooling station, normal radiative heat transfer may suffice to lower thetemperature of the wafer to the point that it can be safely removed fromthe vacuum environment by the end of the cooling cycle. If adequatecooling is not achieved by radiation alone, the problem may bealleviated by the use of the wafer cooling means 118 of FIG. 8, asdiscussed previously in connection with the cooling of wafers at theheating station during rf sputter etch. Once again, the use of gasconduction heat transfer, this time at cooling station 130, may play animportant role in achieving the short cycle time required in theapparatus of this invention.

The final station to which wafer 15 is advanced is the load lock station12, from which the wafer is removed and returned by means of load/unloadassembly 24 to the same slot in the cassette 70 from which it originallycame. The entire load/unload operation was described in detail earlier.

The preferred embodiment of the apparatus of this invention includes aplurality of processing stations for heating, coating, cooling and thelike, and a wafer carrier plate assembly 18 for transporting wafers onan individual basis from station to station. There are many advantageousfeatures inherent in the single wafer concept with the wafer closecoupled and stationary with respect to the deposition source.

For certain applications, an alternative embodiment includes anapparatus in which the wafer or other substrate remains affixed to theload lock door during processing, the wafer carrier plate assembly beingeliminated. A gate valve on the high vacuum side of the load lockprovides communication between the wafer and the deposition source. Atypical operation might include, for example, the steps of: waferloading; wafer heating (or, alternatively, application of r.f. sputteretch); deposition from a sputtering source; wafer cooling; and waferunloading. Gas conduction heat transfer could be advantageously employedto accelerate heating and cooling, and to provide control of wafertemperature during deposition. Although the apparatus of this embodimentlacks some of the versatility and high production rate capability of thepreferred embodiment, it does have several appealing features,including: inherent simplicity and reliability; no wafer transportinside the vacuum system; and the wafer load at risk is at theirreducible minimum of one.

In the preferred embodiment of the apparatus of this invention, thewafer 15 is presented vertically to the inside face of chamber door 22,where it is engaged by vacuum chuck 60. Vacuum chuck 60 and clipactuating means 62 are mounted within chamber door 22. Chamber door 22is the outer door of load lock arrangement 12.

In some applications it may be desirable to separate the waferloading/unloading means from the vacuum sealing means. Accordingly, afurther embodiment is one in which the wafer loading/unloading meansretracts after loading the wafer into wafer carrier plate assembly 18,following which a separate O-ring-sealed door is brought into positionto effect the outer seal for the load lock.

We claim:
 1. Apparatus for processing semiconductor wafers heldstationary during processing, said apparatus comprising:processingchamber means comprising an entrance wall having an entrance opening forwafers; wafer holding means inside said chamber means for holding awafer with one face of the wafer being substantially exposed forprocessing; wafer processing means offset from said entrance opening forprocessing a wafer supported by said wafer holding means, saidprocessing means having a surface adapted to contact a face of a wafer;means for moving said wafer holding means along a first path forpositioning said wafer holding means selectively in alignment with oneor the other of said entrance opening and said processing means, saidmoving means including means for stopping said movement along said firstpath when said wafer holding means is in either of said alignmentpositions; and means for causing relative movement between saidprocessing means and said wafer holding means, one toward the other, ina direction transverse to said first path when said holding means isaligned with said processing means, so that a face of a wafer supportedby said wafer holding means is caused to be in contact with said surfaceof said processing means.
 2. Apparatus as claimed in claim 1 whereinsaid wafer holding means is part of a carrier assembly movably mountedin said chamber means, and said means for causing relative movementbetween said processing means and said wafer holding means in saidtransverse direction comprises means for moving said carrier assemblytoward said processing means.
 3. Apparatus as claimed in claim 1 whereinsaid wafer holding means is part of a carrier assembly movably mountedin said chamber means, said wafer holding means comprises wafer contactmeans adapted to contact a wafer adjacent the periphery of a wafer, andresilient support means extending from said contact means and connectedto said carrier assembly whereby said resilient support means enables awafer to be caused to be in resilient contact with said processingmeans.
 4. Apparatus as claimed in claim 1 wherein said processing meanscomprises means for controlling the temperature of a wafer, saidtemperature controlling means having a substantially circular heattransfer surface, said relative movement in said transverse directionbeing such that a face of a wafer supported by said wafer holding meansis positioned adjacent said heat transfer surface, and said processingmeans being provided with passageway means for introducing gas betweensaid adjacently positioned wafer face and heat transfer surface, andmeans for controlling the temperature of said heat transfer surface. 5.Apparatus as claimed in claim 1 further including a carrier assemblymovably mounted in said chamber means, said carrier assembly having afirst side face said entrance wall and an opposite side facing away fromsaid entrance wall, said wafer holding means being positioned on saidcarrier assembly adjacent the periphery of an aperture in said carrierassembly for holding a wafer aligned with the aperture, so that a wafersupported in said holding means has both faces of such wafersubstantially exposed for processing.
 6. Apparatus as claimed in claim 5wherein said carrier assembly includes sealing means in the form of afirst continuous annular sealing surface surrounding said aperture, saidfirst sealing surface being adapted for sealing contact with a pressuresealing means having a second continuous annular sealing surfacematching said first sealing surface, means for causing relative movementbetween said sealing surfaces to form a seal between said first andsecond sealing surfaces, and wherein said wafer holding means comprisesresilient means positioned inward of said first annular sealing surface,whereby a wafer in said wafer holding means is supported resilientlywith respect to said first annular sealing surface of said carrierassembly.
 7. Apparatus as claimed in claim 5 wherein said processingmeans comprises means for controlling the temperature of a wafer, saidtemperature controlling means being positioned to face said first sideof said carrier assembly; andsaid apparatus further comprises a secondprocessing means, said second processing means being positioned to facesaid opposite side of said carrier assembly.
 8. Apparatus as claimed inclaim 7 wherein said second processing means is in alignment with thefirst said processing means, said second processing means being sputtercoating means having a target for sputter coating a wafer, thearrangement of said temperature controlling means and said sputtercoating means being such that when one face of a wafer on said waferholding means is in contact with said temperature controlling means theother face of the wafer is spaced from said coating target.
 9. Apparatusas claimed in claim 7 wherein said carrier assembly is mounted forrotation around a horizontal axis, said aperture is radially offset fromsaid axis, and said means for moving said wafer holding means along saidfirst path comprises means for rotating said carrier assembly aroundsaid axis.
 10. Apparatus as claimed in claim 7 further comprisingmovable chuck means supported outside said chamber means and adapted toreleasably hold a single wafer; andmeans for moving said chuck means toinsert a wafer through said entrance opening and automatically release awafer directly to said wafer holding means on said carrier assembly whensaid wafer holding means is in alignment with said entrance opening. 11.Apparatus as claimed in claim 10 wherein said wafer holding means onsaid carrier assembly comprises movable means adapted for movementbetween an open position for accepting a wafer and a closed position forholding a wafer.
 12. Apparatus as claimed in claim 11 further comprisingmeans for contacting and thereby moving said movable means, saidcontacting means being mounted on said chuck means.
 13. Apparatus forindividually processing semiconductor wafers having two opposite faces,with said faces oriented substantially vertically and held stationaryduring processing, said apparatus comprising:processing chamber meanscomprising a wall having an entrance opening for wafers; a wafer carrierassembly vertically oriented inside said chamber means and supported forrotation around a horizontally oriented axis, said carrier assemblycomprising at least one aperture, said aperture being radially offsetfrom said axis, said carrier assembly further comprising wafer holdingmeans for releasably holding an individual wafer aligned with saidaperture, said wafer holding means having an open position for acceptinga wafer and a closed position for holding an individual wafer, saidclosed position being adapted to hold a wafer in a manner such that thefaces of the wafer are oriented vertically and the wafer is preventedfrom falling sideways from its vertical orientation; said wafer holdingmeans being supported on said carrier assembly outwardly of saidaperture and having wafer contact means inwardly of the perimeter ofsaid aperture, said wafer contact means being adapted to contact anindividual wafer adjacent the periphery of the wafer so that a waferheld by said wafer holding means in alignment with said aperture hasboth faces fully exposed except for minor peripheral surface areacovered by said wafer contact means; at least two wafer processing meansspaced from said entrance opening and positioned for processing a waferheld on said carrier assembly by said wafer holding means, said twoprocessing means being located on opposite sides of said carrierassembly for processing opposite faces of a wafer; means for rotatingsaid carrier assembly around said axis to selectively position saidaperture in alignment with said entrance opening and said processingmeans, said rotating means being adapted to stop rotation of saidcarrier assembly for holding said aperture stationary at said entranceopening and at said processing means to permit loading and processing ofwafers; and means for causing relative movement between one of saidprocessing means and said wafer holding means, one toward the other, ina horizontal direction when said wafer holding means is aligned withsaid one processing means, whereby a wafer held by said wafer holdingmeans can be placed in contact with said one processing means. 14.Apparatus as claimed in claim 13 wherein said one processing meanscomprises a temperature control surface facing toward said wafer carrierassembly;said apparatus further comprising means for controlling thetemperature of said control surface, said relative movement between saidone processing means and said wafer holding means being such that saidtemperature control surface is positioned adjacent a face of a waferwhen held in said wafer holding means, and means for introducing gasbetween said adjacently positioned control surface and said face of saidwafer from a source outside said chamber means.
 15. Apparatus forindividually processing semiconductor wafers having two opposite faces,and with said faces oriented substantially vertically during processing,said apparatus comprising:processing chamber means comprising two spacedapart walls having surfaces which face each other, said facing surfacesbeing substantially parallel to each other and oriented substantiallyvertically, a first one of said walls being an entrance wall and havingan entrance opening for passage of a wafer therethrough; a wafer carrierassembly mounted between and substantially parallel to said facing wallsurfaces for rotatable movement about a horizontal axis and having afirst side facing toward said entrance wall and a second side facingaway from said entrance wall, said wafer carrier assembly having aplurality of apertures spaced in a circle around said axis, saidentrance opening being located at a position along said circle, wherebyrotation of said wafer carrier assembly can move said aperturesindividually into alignment with said entrance opening; wafer holdingmeans connected to said wafer carrier assembly adjacent the periphery ofeach of said apertures for holding an individual wafer so that the waferis maintained in a substantially vertical position aligned with arespective one of said apertures, and so that both of the opposite facesof the wafer are substantially fully exposed for processing; a pluralityof processing means positioned along the path of said circle ofapertures for processing wafers supported by said holding means, a firstone of said processing means being means for controlling the temperatureof a wafer, a second one of said processing means being means forprocessing one face of a wafer, said first processing means beinglocated adjacent said first side of the carrier assembly, and saidsecond processing means being located adjacent said second side of saidcarrier assembly; means for intermittently rotating said wafer carrierassembly to position a given one of said apertures selectively at saidentrance opening or said processing means; and said first processingmeans comprises a heat transfer surface means, and said apparatusfurther includes means for causing relative movement between said firstprocessing means and said wafer holding means such that a wafer held insaid holding means will have one face of the wafer positioned adjacentsaid heat transfer surface means.
 16. Apparatus for automaticallyprocessing semiconductor wafers, said apparatus comprising:chamber meanscomprising a wall having an entrance opening for wafers; cassette meansoutside said chamber means and configured to hold a plurality of wafers;transfer means adapted to remove a selected wafer from said cassettemeans and position the wafer at an intermediate location outside saidchamber means; movable chuck means adapted to grasp a wafer at saidintermediate location and releasably support the wafer against the forceof gravity; a wafer carrier assembly inside said chamber means andsupported for rotation around a horizontally oriented axis; said wafercarrier assembly being oriented vertically and comprising wafer holdingmeans for releasably holding a wafer against the force of gravity at alocation radially offset from said axis and in a manner such that thewafer is oriented vertically; wafer processing means spaced from saidentrance opening for processing a wafer held on said wafer carrierassembly by said wafer holding means; means for intermittently rotatingsaid wafer carrier assembly around said horizontally oriented axis torotate said wafer holding means into alignment selectively with saidentrance opening and said processing means; means for moving said chuckmeans between said intermediate location and said entrance opening suchthat the chuck means will insert a wafer grasped thereby through saidentrance opening and automatically deliver the wafer directly to saidwafer holding means when said wafer holding means is in alignment withsaid entrance opening; and said processing means comprises means forcontrolling the temperature of a wafer, said temperature controllingmeans having a surface adapted to contact a face of a wafer, and saidapparatus further comprising means for causing relative movement betweensaid temperature controlling means and said wafer holding means to bringa wafer held by said wafer holding means into contact with saidtemperature controlling means.
 17. Apparatus as claimed in claim 16further comprising means for providing gas between said temperaturecontrolling means and the face of a wafer held by said holding means,said means for providing gas being adapted to provide gas at a pressuresubstantially lower than atmospheric pressure.